Extra-oral digital panoramic dental X-ray imaging system

ABSTRACT

An extra-oral digital panoramic dental x-ray imaging system for multi-layer panoramic and transverse X-ray imaging provided with an X-ray source and a digital imaging device providing real time frame mode output and autofocusing. The X-ray source and imaging device are mounted in a mechanical manipulator defining the trajectory of a predetermined image layer. The imaging device communicates with a processor that generates a frames memory from which an image reconstruction mechanism composes the final images.

The present application is a continuation of U.S. application Ser. No.11/673,583 filed Feb. 11, 2007, which was a continuation in part of U.S.patent application Ser. No. 11/277,530 filed 27 Mar. 2006, which claimedthe benefit of prior filed U.S. Provisional Application Ser. No.60/677,020 filed 2 May 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the field of apparatuses and correspondingprocesses involving the use of radiation within the X-ray spectrum withspecific features characteristic of X-ray applications. Morespecifically, the present invention relates to digital dental panoramicimaging apparatuses producing a digital image of a curved dentalstructure, wherein a digital image of all teeth on upper and/or lowerjaws is formed in a single digital image.

2. Background of the Invention

Dental panoramic X-ray imaging is a well-known dental radiographicprocedure. Its purpose is to produce an X-ray image of the entire jawfor diagnosis as opposed to a partial image such as obtained byintra-oral X-ray imaging. Other extra-oral dental X-ray imaging systemsinclude cone beam dental computed tomography (CT) system for 3-Dtomosynthetic volumetric reconstruction and transverse slicing. Regularpanoramic imaging is used mostly from general purpose orthodontics,while 3-D imaging and transverse slicing maybe used more often fordental implantation.

Dental panoramic X-ray imaging units, cone beam units and transverseslicing units, a.k.a. orthopantomographs (OPGs) or dental CT's, areavailable with analog film were suitable and with digital sensors (incase of cone beam CT). Digital OPGs currently available in the marketutilize sensors based on CCDs coupled to a phosphor or scintillator, andoperate in a Time Delay Integration Mode (TDI), or flat panels utilizinga-Si (amorphous silicon) TFT arrays (Thin Film Transistor) with again ascintillator on the top. Both CCD's and TFT flat panels used convertx-rays to light and then light is converted to an electronic signalinside the CCD or TFT. This equipment and especially the cone beam CTand transverse slicing equipment which produce multiple frames, thesesystems are not fast enough for continuous exposure. Consequently, realtime viewing is not possible. A fully equipped dental office needs tohave several types of so called “intra-oral” sensors to complete therange of functionalities needed to cover general maxillofacialexaminations, fillings and cavities, orthodontics, implantology andsurgery. As can be appreciated, this is a cost burden that probably onlylarge clinics can afford.

An orthopantomograph is made up of four functional units: an X-raygenerator; an imaging device; a mechanical manipulator; and a usercontrol panel. The purpose of the X-ray generator is to create thex-rays that penetrate the head of the patient and arrive at the imagingdevice. The X-ray generator or source is able to generate x-rays withdifferent spectra by varying the high voltage level and with differingintensity by varying the current. The imaging device detects andconverts the x-rays incident on it into an image. The mechanicalmanipulator displaces both the imaging device and the X-ray generator insuch a way that a proper panoramic image of the plane-of-interest isformed. The user control panel or the user interface, is used to controldifferent settings of the OPG or to initiate and control an X-rayexposure event.

Currently digital imaging devices accomplish their purpose through:absorption by traditional films, or by digital two-stage indirectconversion (using a CCD with a scintillator). Linear arrays of CCD's areused in OPG's but flat panels based on TFT or image intensifiers areused in cone beam dental CT. A typical cone beam dental CT system doesnot differ in any substantial way from the OPG system, except that theX-ray beam is cone shaped rather than fan shaped. Additionally the conebeam systems require that the X-ray scan be performed for longer timesand in step fashion (i.e., not continuously) because Image Intesifiers(IIs) or TFT panels are too slow and lack sensitivity.

Dental Panoramic, Dental Transverse and Dental 3-D X-Ray Imaging

In dental panoramic X-ray imaging, the image is captured during aprocess in which both the X-ray generator and the imaging device movearound the patient's head according to a predetermined geometric pathand speed profile. The movement is synchronized in such a way that animage of the pre-determined layer of interest is formed according to thepredetermined geometry and speed profile. Because of the shape of thehuman jaw, this layer is a non-planar structure. It in fact varies withthe morphology of each individual's jaw. To simplify the procedure whilestill maintaining high resolution, a standard shape is used that isapplied to all human males, females, and children of certain ages, isused. The exact shape of the layer-of-interest depends on the dentalprocedure in question; the predetermined geometric path of the sourceand detector (optionally varying depending on the patient type); and thepredetermined speed profile. The layer can usually be adjusted byselecting a different pre-determined, preset program in the OPG bychanging the path of movement and/or also the speed profile. Differentprograms can alter the general parameters of the profile to match thepatient (again, e.g., whether child or adult) or to only image a part ofthe full profile (i.e., front teeth, left/right side etc.). But in eachcase when a new panoramic layer is needed a new exposure needs to betaken, which means additional radiation to the patient.

The movement of the X-ray generator and the imaging device istraditionally synchronized so that the imaging device surface normal isperpendicular to the layer-of-interest. In this way the formed image isdistorted as little as possible. A disadvantage of this approach is thatthe movement trajectory is quite complex. To achieve this motion,multiple motors are required (i.e. degrees of freedom) which alsocomplicates the control electronics and algorithms, thus leading tohigher cost. There are some imaging modalities in which the direction ofradiation is intentionally not perpendicular to the surface normal, butthe same drawbacks and advantages apply. In addition, one of the mostsevere issues experienced today in clinical applications of dentalpanoramic imaging is that the patient (object) does or cannotnecessarily remain motionless for the whole duration of the scan(typically lasting 5 to 30 seconds). Even a small misalignment of thepatient can result in that the part of the imaged layer being blurred orout of focus. In addition to panoramic images, a dentist may wish tocreate a transverse slice image of the patient's jaw. In transverseimaging, the layer-of-interest is perpendicular to the panoramic layer.

The existing commercially available, extra-oral (including, for example,panoramic and transverse) imaging solutions are either based onelongated (i.e., with an aspect ratio—length “m” divided by width “n”—ofm/n=5 or more) time-delayed integration CCD sensors (not producingmultiple frames) or on large-area 2D detectors with a computedtomography system backend where m/n is substantially equal to 1 (which,however, do produce multiple frames). The large-area 2D detectors aremost often TFT panels and are particularly expensive because of them/n.apprxeq.1 aspect ratio (approximately equal to one). The elongateddetectors, which use a CCD coupled with a scintillator, apply thetime-delayed integration (TDI) principle to form the image of the layerof interest. Time-Delay Integration is a method of synchronizing theshifting of the image signal captured in the pixel with the movement ofthe object image across the face of the CCD. This permits integration ofmore signal, increasing sensitivity, reducing noise and reducing imageblur. According to this method, the integrated charges are clockedinside the detector logic (CCD) in the direction of the movement. Thus,at a given integration period t_(i), the charge for a fixed objectvolume v is integrated to a pixel p_(n). The object is moved so that theimage of the plane-of-interest is moved (taking the magnification factorinto account) exactly a pixel's width. After the integration period, thecharges are transferred in such a way that if the image of the volume vis projected to pixel p_(i-1), the charged from pixel p_(i) istransferred to pixel p_(i-1). The last pixel value in the row, which hasno neighbor to which to transfer the charge, is read out and stored inthe final image. In this way, the apparent integration time of an imagepixel is the integration period multiplied by the width of the imagingdevice in pixels.

With the TDI principle, the clocking of the charges must be synchronizedso that the apparent speed of the layer-of-interest in the imagingdevices active in an integration period must be exactly the width of thepixel. If the speed is not matched, the image will appear blurred. A 2Dflat image is formed from a single scan using an imaging deviceoperating in the TDI mode. Multiple panoramic layers, transverse slicingor 3D imaging is not possible because only a single projection is saved.

In a dental cone beam computed tomography system (3-D imaging),multiple, non-TDI exposures are taken with a 2D area detector where msubstantially equals n (i.e. within 20%). The movement is stopped beforethe exposure and the X-ray source is only active during this stationaryperiod. The movement is continued after the exposure. In this manner,the movement doesn't have to be synchronized. Such systems require ahigher dose to be administered to the patient and also longerexamination times. The final image is formed as a layer calculated fromthe volumetric (3D) dataset constructed from the individual exposures orprojections. The clear advantage of this method is that a full 3Dvolumetric dataset will be available after the procedure. However, withcurrent solutions, the resolution of panoramic layer calculated from the3D data is low compared to dedicated panoramic imaging systems (OPGs).Furthermore, the dose levels are much higher and maybe equallyimportantly the cost of such available systems is in the range of 200kUSD-400 kUSD.

U.S. Pat. No. 6,496,557, entitled “Two Dimensional Slot X-ray BoneDensitometry, Radiography and Tomography,” describes a process in whichmultiple layers are formed by a so-called shift-and-add algorithm. Theprocess described includes a system in which the motion of the imagingdevice is either linear or includes a rotational component around thefocal point of the X-ray source. Unfortunately, such a system cannot beused in the field of dental X-ray imaging where the layer(s) of interestrun around or across the human jaw. Although such an approach may beuseful in bone densitometry and in some other applications, it is inpractice impossible to apply to dental panoramic or transverse imagingdue to the fact that x-rays run essentially parallel to rather thanacross the layer-of-interest, should there be linear movement orrotation around the focal point. Additionally, the process disclosed inU.S. Pat. No. 6,496,557 would have another serious limitation if anattempt were to be made to apply it in the field of dental imaging. Thatlimitation is the most serious issue in panoramic imaging and it resultsin partial image blurring due to misalignment of the patient or due topatient movement. Also, U.S. Pat. No. 6,496,557 fails to address theneed of a system or a procedure that is able to simultaneously performboth panoramic as well as transverse imaging. Further, this patent failsto disclose a system operable in a dental imaging environment.

U.S. Pat. No. 5,784,429, entitled “Dental panoramic X-ray imagingapparatus,” describes a system in which multiple layers are calculatedusing plural tomographic images corresponding to plural tomographicplanes which are arranged at predetermined intervals along the directionof the X-ray irradiation. A convolution process or a frequency processis conducted on a specific tomographic image by using image informationof at least one of the tomographic images, so as to remove blur from thespecific tomographic image. This patent describes a means ofimplementing different layers by using image intensifiers, CCD's orcombinations thereof.

U.S. Pat. No. 7,136,452, entitled “Radiation Imaging System and ScanningDevice,” discloses the use of frame mode CdTe-CMOS detectors forcreating tomographic images in several applications including dentalpanoramic images using a dental X-ray setup. In U.S. Pat. No. 7,136,452,Spartiotis et al. disclose that the read-out speed or frame rate must behigh enough to allow the detector to move by no more than half a pixelsize or preferably even less per a read-out cycle. Emphasis added.However, if a system is implemented in such a way, serious limitationscan arise such as the need to transfer a disproportionately large amountof data to a computer or the like in real-time. However, '452 patent issilent on the management of data to reconstruct and display an image inreal-time, during the exposure. Furthermore, Spartiotis et al. teachnothing about one of the most serious issues facing dental radiology,that of partial image blurring due to patient misalignment and how tocreate automatically a focused layer. In such cases, part of the image(i.e., the panoramic layer-of-interest) is blurred while another part isin focus. Spartiotis et al. merely disclose that the frame rate needs bevery high to collect frames in such a case in which the detector hasmoved by less than half a pixel, but does not teach how to accomplishthis. Unfortunately, in this case, the amount of data produced duringthe exposure is unnecessarily high while at the same time, no materialperformance benefit is gained. Additionally, Spartiotis et al. do notsuggest a means by which one might combine data to gain performancebenefits and to correct blurring or to produce transverse image slicesor even tomosynthentic 3D images.

Devices exist that are capable for example of performing transverseslicing or 3-D reconstructed images, but most often they require muchlonger X-ray scan times and non-continuous scan (i.e., a step by stepscan). The long exposures are needed because the normally used digitalimaging devices lack sensitivity and typically can “catch” only 1 out of3 incoming x-rays. Further, non-continuous step-wise scans are necessaryin the prior art because of the slow response and slow readout of thecurrent rectangular or square flat panel TFT arrays. Higher doses andlonger step-wise scans create higher risk and discomfort to the patient.

Additionally, the prior art does not suggest a means by which one mightcombine data to gain performance benefits and to correct blurring or toproduce transverse image slices or even tomosynthentic 3D images. Whatis needed, therefore, is a system that limits the radiation doses apatient receives while maximizing the data output. Further, what isneeded is a system which permits continuous fast, real-time X-ray scans,and a system and method of combining data from a single exposure to, notonly reconstruct a panoramic layer of interest, but to also be able tocorrect part of the image that is blurred and furthermore producetransverse image slices and 3D images. Still further needed is a systemthat is capable of correcting blurring and which can produce transverseimage slices or tomosynthentic 3D image.

SUMMARY OF THE INVENTION

The present invention is an extra-oral dental X-ray digital imagingsystem. The present system produces digital panoramic extra-oral dentalX-ray images, including multi-layer dental panoramic and transverseX-ray images. The system includes an X-ray source, a digital imagingdevice having a frame mode output capable of a high frame rate, amechanical manipulator having at least one rotation axis located in aposition other that the focal point of the X-ray source and means ofdetecting the camera position in 1D, 2D or 3D depending of thecomplexity of the trajectory and means of reconstructing the finalimages out of the stored frames. Also included are a real time storagesystem such as RAM, a hard drive or a drive array able to store all theframes captured during an exposure, and a digital processing unitinterconnected in operational arrangement with the other components andcapable of executing the reconstruction algorithm. The present system isadapted to produce selectively two or more of the following: 1) apredetermined dental panoramic layer image 2) at least part of a nonpredetermined dental panoramic layer image 3) transverse slice to aselected part of a dental panoramic layer image 4) 3-D reconstruction ofa volume corresponding to some part of a dental panoramic layer, allfrom image data from a single exposure.

In particular, the system combines a fast readout with a memory ofcomparable speed, i.e., a memory which stores and accesses informationsubstantially in any order and in which all storage locations aresubstantially equally accessible. Such a memory has sufficient speed forstoring the multiple frames concurrently with the exposure in a mannerwhich permits retrieval and display in real time. Preferably such systemshould employ an X-ray imaging device having an aspect ratio of m/n>1.2where m is the long dimension and n is the short dimension of the activearea of the imaging device. In accomplishing its advantages, the presentsystem causes substantially no greater radiation exposure than the doseused in a regular dental panoramic exposure, while performing the X-rayscan to collect such data in a continuous movement. Additionally, thedetector device produces a variety of formats of panoramic images from ahigh-speed, X-ray digital imaging device. In a further advantage, thepresent system and method combines data from a single exposure to notonly reconstruct a panoramic layer of interest but to also be able tocorrect part of the image that is blurred and furthermore producetransverse image slices and 3D images.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an X-ray photograph of a sample dental panoramic X-ray imageproduced using the present invention.

FIG. 2 is a schematic view of a dental panoramic X-ray imaging system.

FIG. 3 is a schematic view of a lower jaw bone illustrating a panoramiclayer-of-interest.

FIG. 4 is a schematic view of a lower jaw bone illustrating a transverseslice across a point on a panoramic layer-of-interest.

FIG. 5 a is a schematic view of the readout and recording of an imageusing a prior art TDI-type device which records only a single layer byoutputting image lines using the CCD TDI technique during the X-rayscan.

FIG. 5 b is a schematic view of the readout in accordance with thepresent invention and recording of an image using a high-speed X-raydigital imaging device that outputs many independent overlapping frames.

FIG. 6 a is a drawn example of a high speed CdTe-CMOS X-ray digitalimaging device in accordance with the invention that outputs manyindependent image frames.

FIG. 6 b is a schematic representation of a CdTe-CMOS hybrid which wasused to construct the imaging device of FIG. 6 a in accordance with thecurrent invention.

FIG. 7 is a schematic view of the reconstruction of an image inaccordance with the present invention using the frames from thehigh-speed X-ray digital imaging device by means of >0.5<1 frame shiftand addition of the individual frames.

FIGS. 8 a-b is a flow chart of the Time-compensated laminographicreconstruction (shift-and-add submethod) of the invention.

FIG. 8 c is a schematic diagram of pixel signal value integrationintervals over time.

FIG. 9 is a flow chart of the auto-focusing feature of a panoramic layerin accordance with the invention.

FIG. 10 is a flow chart of the feature of the present invention forcalculating a transverse slice at a point on a panoramic layer.

FIG. 11 is a flow chart of the feature of the present invention forcalculating a 3-D image at point on a panoramic layer using a narrowbeam, limited angle 3D reconstruction.

FIG. 12 is a graphical representation of the optimization of the speedprofile.

FIG. 13 is a top, schematic view of an example of a panoramic,transverse layer formed by concatenating rows from multiple panoramicimages from the same location.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, the details of preferred embodiments ofthe present invention are graphically and schematically illustrated.Like elements in the drawings are represented by like numbers, and anysimilar elements are represented by like numbers with a different lowercase letter suffix.

Referring to FIGS. 1 and 2, the system 10 of the invention uses a framemode CdTe-CMOS detectors for creating tomographic images includingdental panoramic images using a dental X-ray setup. In this application,the read-out speed or frame rate need only be high enough to allow thedetector to move by more than half a pixel size and preferably less afull pixel read-out cycle. However, serious limitations can arise suchas the need to transfer a disproportionately large amount of data to acomputer or the like in real-time. Therefore, it is beneficial to managedata in order to reconstruct and display an image in real-time, duringthe exposure.

The dental X-ray imaging system 10 produces panoramic images 12 for usein dental diagnosis and treatment. The system 10, using data generatedfrom a single exposure, selectively produces at least two of thefollowing: 1) a predetermined dental panoramic layer image 2) at leastpart of another dental panoramic layer(s) 3) transverse slice to aselected part of a dental panoramic layer image 4) 3-D reconstruction ofa volume corresponding to some part of a dental panoramic layer.

The system 10 preferably employs a detector having an aspect ratio ofits long m to short n dimensions in its “active area” with an m/n ratiogreater than 1.5. The “active area” is the portion of the X-ray imagingdevice that is sensitive to detecting X-ray flux. This is advantageousbecause such a detector is much more economical and practical than afull square area detector. Although digital detector prices aredropping, it is still the case that a full field digital imaging devicehaving sufficient resolution is much more expensive than an elongatedimaging device. In a preferred embodiment, the present invention uses adigital imaging device having detector substrate made of a Cadmium andTelluride composition, such as CdTe or CdZnTe (Cadmium Zinc Telluride).Additionally, it is preferred that the detector is bump-bonded to areadout substrate, e.g., a Complementary Metal Oxide Semiconductor(CMOS) Application Specific Integrated Circuit (ASIC). CdTe and CdZnTedetectors bump-bonded to CMOS ASIC are preferred as suitably fast X-rayimaging devices, due to their high density and absorption efficiency,readout speed and resolution.

The dental X-ray imaging system 10 in accordance with the presentinvention includes an X-ray source 16 for generating the radiation to bedetected by the digital imaging device 14. The digital imaging device 14has a frame mode output with a sufficiently high frame rate as set forthbelow. A mechanical manipulator 20 mounts hardware of the source 16 andimaging device 14. The mechanical manipulator has at least one rotationaxis located in a position other that the focal point of the X-raysource, and includes an alignment estimator 24. A reconstructionalgorithm 26 (see FIGS. 8 a-8 c) reconstructs at least two final digitalimaging device 14 images out of the same set of stored frames 40 (seeFIG. 5 b) from a single exposure. A storage system 17 is used totemporarily storing all the data in effectively real time, and aprocessing unit 22 such as a personal computer, is used to controlcertain processes of the system 10.

The X-ray source 16 is a radiation source such as an X-ray generator ora radionuclide. The X-ray source 16 irradiates an object 19 to beimaged. The X-ray imaging device 14 is adapted to produce multipleframes 40 during at least part of the exposure/irradiation period. Themechanical manipulator 20 controls the movement of the X-ray source 16and the imaging device 14 about at least one rotation axis along aspline, which may of course, be a circular or non-circular trajectory.The axis is located somewhere between the X-ray source focal point andthe X-ray imaging device. The reconstruction algorithm 26 uses themultiple frames 40 to compose a panoramic image of a layer of the objectunder observation, the image having a focus depth which is different inat least some part of the panoramic image from the focus depthcorresponding to a predetermined panoramic image.

The present invention is a scanning X-ray imaging system 10 wherein theX-ray source 16 is adapted for transmitting X-rays and exposing anobject position to the x-rays. The object position 70 is a location thatan object to be imaged is position for exposure to the X-rays, and isdisposed between the X-ray source 16 and the X-ray imaging device 14.The combination of the X-ray source 16 and the imaging device 14 trackalong a path defined within the object position 70 over the course of anexposure cycle. This defined path corresponds to the pre-determinedimage layer speed profile. The scanning X-ray imaging device 14 isadapted for receiving transmitted X-rays and for producing multipleimage frames during at least part of the exposure cycle. As the imageframes 40 are produced, they are held/stored as corrected raw pixelsignal data. If real time imaging is desired, the image frame data areheld in a “fast” storage medium 17, otherwise they are held in anotheradequate storage medium.

Individual frames and groups of frames can be selectively recalled fromthe held/stored image frames 40. A selectable portion of the imageframes 40 are selectable for use by a means that automaticallyreconstructs a focused tomographic image from two or more image layerspeed profiles. An algorithm is used as the means that reconstructs afocused tomographic image. The user selects a region of interest (e.g.,of the predetermined layer panoramic image) that it is desired torefocus. The algorithm accomplishes automatic refocusing by optimizingthe image sharpness of the selected region of interest by doing asharpness comparison between appropriate multiple frames with differentspeed profiles, which are otherwise analogous to the region of interestand replacing the region in the image with the sharper analogous region.

The digital imaging device has active area dimensions m×n, wherein m isthe long dimension 530 and n is the short dimension 510 (see FIG. 6 a)such that m/n>1.5 thus it has an elongated shape and is able to readoutthe frames 40 at 50 fps (frames per second) or more preferably 100 fpsand even more preferably 300 fps or more. The m/n>1.5 geometry helpskeep the costs of such a device down and indeed costs can be much lessthat a full field active area imaging device. This is particularly truewhere the imaging device is a CdTe-CMOS 560 or CdZnTe-CMOS imagingdevice.

Furthermore, the mechanical manipulator's X-ray source arm 20 anddigital imaging device 14 move in a continuous scan movement (notnecessarily constant) for the duration of the useful part of the scan,i.e., the part of the scan that x-rays are emitted from the X-ray source16 as needed to image substantially the whole jaw 19. The duration ofthe scan and the amount of x-rays emitted are comparable to theradiation dose required in a regular dental panoramic X-ray scan. Thefinal images can be selected from a group of predetermined panoramiclayer images 99 (see FIG. 13), other panoramic layers images (or atleast part thereof 98), transverse slicing images, or 3-D images.

A real time storage device 17 such as RAM 18 (or a similarly fast datastorage & access device) is used to store-and-hold all the frames 40captured during an exposure. A digital processing unit 22 (for example,a typical computer CPU) is in electronic communication with the realtime storage device 17 and executes the reconstruction algorithm usingthe frames 40 (corrected raw pixel array signal data) held on thestorage device 17. The system 10 selectively produces dental panoramicX-ray images 12 or parts thereof, dental transverse X-ray images 224 anddental tomosynthetic 3D images from a frame stream produced by thehigh-speed, X-ray digital imaging device.

The imaging device 14 is a digital imaging device is a “frame mode”output device (as opposed to a “line” output device), outputtingcorrected raw frame data in frame mode output with a sufficient fastframe rate. This means that the imaging device is disposed to movesubstantially continuously relative to the object being scanned, andthat the individually addressable imaging cell output values are readoutat time intervals substantially corresponding to a point on the objectimage traversing between half and the full distance w of a detectorpixel in the scanning direction during a scan. That is, that on average,frame shift intervals are more than half a pixel width (i.e., w/2=>0.5)in the direction of the scan, but less than a full pixel width s,averaged over all the frames in an exposure.

A working embodiment of the present imaging device 14 is of the typeshown in the photo in FIG. 6 a. The elongated active area 520 of theimaging device comprised six CMOS/detector hybrids. FIG. 6 bschematically illustrates such a CMOS/detector hybrid. The preferreddetector substrate 620 illustrated comprised a Cadmium and Telluridecomposition, such as CdTe and CdZnTe, which absorbs the X-rays withextreme sensitivity and converts them directly to an electronic charge.The CMOS readout substrate 630 was in electrical communication with thedetector substrate 620, by means of low temperature lead free solderbumps 610 (see U.S. Pat. No. 6,933,505). The individual CMOS/detectorhybrids are connected electrically to the mother board 560 by means ofwire bonding of pads 640 onto the corresponding pads of the motherboard. Beneath the mother board 560 there is situated a readout orinterface board 570 for controlling the mother board and producing adigital video signal which is readout via connector 550. Connector 550can be of the camera link type protocol which is a commerciallyavailable readout protocol. Nevertheless, the readout can also happenthrough a variety of other readout protocols such as USB 2.0, firewireor gigabit Ethernet. The interface board also contains a power supplyconnector 540 which provides all the necessary supply voltages to theboards as well as High Voltage (“HV”) to the CdTe detectors. A framemode imaging device 14 in accordance with the invention producesindependent image frames 40 by means of outputting sequentially or inrandom access, pixel values every so often and usually in predeterminedtime intervals.

A frame 40 is understood to be a two dimensional spatial representationof pixel values 55, each pixel value 55 corresponding to the output froma physical pixel 53 in the imaging device or in some cases each pixelvalue 55 can correspond to a combination of output values from theimaging device physical pixels 53. The conversion of the output signalof an image device pixel 53 to its corresponding frame pixel value 55can take place inside the imaging device or externally, for exampleinside the computer 22. The imaging device 14 is able to produce manyindividual frames 40 during the X-ray scan, with very high sensitivity.In a regular CCD based panoramic examination, the CCD works in the TimeDelay Integration mode (TDI) which is well-known in the field. Theoutput from a CCD imaging device is image lines 110 as depictedschematically in FIG. 5 a. For the duration of the scan, the CCD outputsimage lines 110 and at the end of the scan only one panoramic imagelayer 12 is reconstructed corresponding to a predetermined layerdepending on the mechanical geometry of the panoramic unit and the speedprofile and the positioning of the patient.

On the other hand, the imaging device 14 of the type described in FIGS.6 a and 6 b operates in frame output mode, with sufficient speed andexcellent sensitivity to match the speed. The imaging device implementedby the applicant operates at frame rates of 50 fps to 300 fps or moredepending on the mechanical scanning speed of the X-ray source. As shownin FIG. 5 b, during the X-ray scan the output from the imaging deviceare frames 40 rather than lines, such frames 40 overlapping during thescan and providing the necessary data redundancy needed to reconstructnot only one but several dental panoramic layers, or parts of layers,transverse slicing and even 3-D tomosynthetic image reconstruction ofteeth. The imaging device of FIG. 6 a can also provide just rawindependent pixel values and in this case, the frames 40 may bereconstructed then in the personal computer by rearranging the pixelvalues to frames.

The mechanical manipulator 20 has at least one rotation axis 34 locatedin a position other that the focal point 36 of the X-ray source. Thealignment estimator 24 detects the camera position in 1D, 2D or 3Ddepending on the complexity of the trajectory. The panoramicreconstruction process 26 uses an algorithm to reconstruct the finalimages 12 out of the stored frames 40. The storage system 17 is capableof storing the frames 40 in real time in order to avoid frame loss andis therefore essentially a real time storage system such as RAM 18, orvery fast hard drive or an drive array capable of transferring storeddata at 10 MB/sec or faster and therefore able to store all the frames40 captured during an exposure while permitting real time retrieval ofsuch data. In a preferred embodiment, RAM 18 having a 50 MB/secretrieval rate is a Kingston 400 MHz 2 GB DDR (model number KHX3200AK2/2G). This RAM has a clock speed of 400 MHz and with every clockpulse it is able to store 8 bits. Models with RAM speeds of 5 GB/sec ormore are available. These storage means may be located in the computer22 or located in the imaging device 14 or at some other location.Storing frames 40 in real time here means with a time delay of not morethan few seconds and preferably few milliseconds and even morepreferably few microseconds. The processing unit 32 is a digitalprocessing unit such as a personal computer 22, micro controller, FPGAor DSP, (not shown) capable of executing the reconstruction algorithm26.

Referring now to FIGS. 3 and 4, the speed of the X-ray imaging device 14combined with the reconstruction algorithm 26 allow formation ofmultiple dental X-ray images from the frames 40 of a single exposure. Asingle exposure refers here to a continuous measurement in which thewhole layer-of-interest 52 (the layer-of-interest can be a part of thewhole dental area) is exposed to radiation one or more times, but inwhich the apparent movement between two consecutive radiated frames 40is never less than half the size of a pixel 53 and stays less than thefull size w of the pixel 53. This results in there being ample overlap56 between consecutive frames 40, but not at the expense of creatinghuge data sets that cannot be utilized in real time. This isparticularly important in dental imaging where the user (dentist) isexpecting to see an image 12 in effectively real-time and during theexposure.

Note that “Effectively Real-Time” as used herein means that the image 12is displayed in less than 10 seconds after the end of the exposure andmore preferably less than 5 seconds, and optimally, the image isdisplayed effectively simultaneously during the exposure. For this to beachieved, the frame rate or time intervals between consecutive frames 40must not be shorter than what is needed to allow the physical pixels 53to move by at least half a pixel width-size s, but short enough to havethe detector pixels 53 move less than a full pixel width size s.Regarding such imaging devices 14 as were described herein withreference to FIGS. 6 a and 6 b, capable of producing multiple frame datawith the above qualities, see WO2004055550 and EP 1520300.

The imaging device 14 and radiation source 16 of the present system 10rotates around an axis 34 which is positioned between (but notnecessarily crossing the volume of x-rays 35 from the source 16 to theimaging device 14) the X-ray source 16 and the imaging device 14.Furthermore, the frames 40 generated by the (CdTe-CMOS/CdZnTe-CMOS)imaging device 14 are temporarily stored in real time in a sufficientlylarge RAM 18, to allow real time processing and display of a dentalpanoramic image 12 of a layer 52. That is, a “reconstructed” or readableimage begins to be presented (unfolds) for the viewer before theexposure cycle is fully completed. The processing of the frames toproduce such panoramic images 12 includes spatial (i.e. pixel) domainarithmetic.

The difference between a normal TDI-type device (not shown) and thepresent imaging system 10 is illustrated in FIGS. 5 b and 7. A normalTDI-type device records only a single layer 12, while the present system10 records multiple overlapping frames 40 which can be used to calculatemultiple layers (both panoramic and transverse) and limitedtomosynthetic 3D structures.

Referring now to FIGS. 6 a and 6 b, the imaging device 14 itself has anaperture 520 which is elongated (i.e., has one edge 530 which is muchlonger that the other edge 510). In this particular embodiment, one edgeis 0.6 cm in width and the other is 15 cm in length. The device 14 hasan active area made of an array of 1500.times.64 pixels. The detectoractive area 520 is made of six CMOS/detector hybrids and combinedprovides the active slot 520 which has two main dimensions: m and nwhere m is the long dimension 530 and n is the short dimension 510. Ascan be seen, m/n>>1. Preferably m/n>1.5, and even more preferably m/n>5and even 10. In the embodiment disclosed in FIG. 6 a, the ratio m/n wasgreater than 23. An important benefit of the preferred ratios achievableby the present system 10 is that: the larger the active area, the moreexpensive the detector is. For example, even with current mass producedflat panel TFT arrays, the price of an imaging device with m/n=1 orclose to 1 is of the order $20,000 or even $30,000 USD. However, with animaging device 14 of the present system 10, one is able to have thefunctionalities of regular panoramic equipment as well as at leastpartly, the functionality of the very expensive transverse slicing and3-D reconstruction dental equipment.

The combination of the imaging device 14 and X-ray generator 16 rotatearound the object position 70, i.e., the head of the patient 72, but theangular coverage can be less that a full circle as compared to a CTsystem (not shown). The position of the imaging device 14 is eitherrecorded as a one-dimensional position counter which tells the positionof the current frame 40 in the final panoramic image 12, or it canrecord the full 3D position including orientation. The system 10 recordsthe relative position of the imaging device 14 as a function of time,and thus it is possible to reconstruct a full dental image 12 fromindividual frames 40 stored. Referring again to FIG. 1, the simplestreconstruction is the one for producing a dental panoramic X-ray image12. In this case, the position of the current frame 40 is recorded as acoordinate 74 in the final image 12. This coordinate 74 is then used tocalculate the shift 76 required in a shift-and-add algorithm, mentionedabove as the reconstruction algorithm 26 used in reconstructing thefinal image.

Referring again to FIGS. 8 b and 8 c, the sub-pixel shifting isaccomplished by adding the pixels 55 in a frame 40 to two locations inthe final image 12 multiplied by suitable weighting factors w_(left),w_(right). If the target position is x (non-integer or integer) and theposition is increasing in a positive direction, then the pixel value 55is added to positions floor(x) and ceil(x) where floor(x) refers to thelargest integer smaller than x and ceil(x) refers smallest integerlarger that x. The respective weighting coefficients w_(left), w_(right)are x-floor(x) and ceil(x)-x. The weighting factors w_(left), w_(right)can be global to a single frame 40, or can vary from pixel to pixel tocompensate for any time delays between individual pixels. This ismathematically equivalent to interpolating the frames 40 and final image12 linearly in the horizontal direction, shifting the frame pixels inthe horizontal direction by an integer amount and then down-sampling theframes 40 and the final image to the original size. The sub-pixelshifting can also be implemented using any other interpolation method,for example with bi-linear, bi-cubic or spline interpolation. Thesub-pixel shift-and-add algorithm 26 is implemented to eliminate extrajaggedness of diagonal edges compared to an integer shift-and-addalgorithm (i.e., only use integer part of the position 86 without anyinterpolation or weighing).

Referring now to FIG. 9 an algorithm 300 is provided which auto-focusesa panoramic layer and automatically calculating the layer-of-best-focusfor dental panoramic imaging. The algorithm 300 uses the multiple frames40 to compose a panoramic image of a layer of the object underobservation, the image having a focus depth which is different in atleast some part of the panoramic image from the focus depthcorresponding to a predetermined panoramic image. The algorithm 300 hasfive steps. In a first step 302, frame data 304 is used to reset thechange in velocity ΔV of movement in the image plane compared to thechange in original velocity ΔV_(orig). In a second step 306, the userspecifies a region of interest. In a third step 310, the region ofinterest is reconstructed at the original speed V_(orig) plus the changein velocity ΔV. In a fourth step 312, the sharpness measure S_((n))(sharpness measure S, which can either be a measure of contrast,roughness or some other measure of the image sharpness) and sharpnessdifference ΔS is calculated as being equal to S_((n)) minusS_((n-1))×SM(Vorig+ΔV). In a fifth step 314, if ΔS is less than aparticular limit, then the region of interest is displayed. Otherwise,calculate using a different step delta velocity ΔV and returns to step310 and continue. The algorithm 300 can be applied globally to the wholefinal image 12 or locally to a given region-of-interest 98. Therefore, auser of the system 10 (e.g., a dentist) is able to observe and initialpanoramic image 12 and then select a region (portion) 98 of the image 12where blurring may be evident, in which case, the algorithm maximizessharpness S of the selected part of the image. The result is a completeimage 12 with all parts well in focus.

By reversing the direction in which the frames 40 are added to the finalimage 12, a completely different layer 60 can be reconstructed. By usingthe same speed profile 186, but reversed a direction, a mirror layer canbe reconstructed. This mirror layer is on the opposite side of thepatient, and in the dental panoramic imaging this equates to the area ofthe neck in the center part of the scan. So the invention provides amethod to calculate the image of the spine. By re-projecting this imageto the normal panoramic layer (by flipping the mirror image and applyingsuitable re-scaling function), an estimate of the blurring caused by thespine is obtained. This estimate can then be subtracted from thepanoramic image 12 to decrease the effect of the spine on the imagequality. As an end result, the panoramic image 12 is obtained withoutany potentially distracting superfluous images of the spine structure.

Example I

For typical a dental application of the present system 10, the elongatedCMOS/detector sensor had an active slot 520 (FIG. 6 a) of 150 mm×6.4 mmin size. The pixel size w in the scanning direction was typically 100um, although smaller pixel sizes are achievable (but considered asunnecessary in dental extra-oral imaging). The exposure scan time was 5to 30 seconds, with a frame rate of 200 to 300 fps (frames per second).The sensor moves about half a pixel size to less than one full pixelsize w between consecutive frames 40. At that rate, the output framedata 304 can reach more than 750 MB for the entire scan which is a largedata set, but still is quite manageable. It is essential therefore thatthe frame rate not be too high as this would not add anything to theimage resolution and would only make data transfer and processingdifficult, if not impossible, in real-time.

A video or frame grabber, based on a technology such as “CAMERALINK”™,was installed to a PCI Express slot of the PC 22 and used to captureframes 40. The frames 40 are then stored temporarily in RAM 18. This isvery important, because otherwise it would be very difficult, if notimpossible, to store and process 750 MB of data and display an image 12that is reconstructed from such a large data set in real-time. Inaccordance with the present invention, the use of computer RAM 18enables temporary storage of data.

Referring in particular to FIGS. 8 a and 8 b, the shift-and-addsubmethod of algorithm 26 is a fast processing method for reconstructingand displaying a panoramic layer 12 in real-time, and includes thefollowing steps. In a first step 26 a, the final image 12 is initializedwith zero values. In a second step 26 b, all the collected frames 40 arethen processed one-by-one in the following manner: in a first substep 26b′, for each frame pixel in an individual frame, the pixel position 86is calculated. In a second substep 26 b″, weighting coefficients arecalculated according to FIG. 8 b. In a third substep 26 b′″, the pixelvalue multiplied by the weighting factors is added to the pixel value ofthe final image 12 in locations specified in FIG. 8 b.

Additionally, the system 10, can comprise a dedicated or separateprocessing device, for example incorporated within the imaging device14, where the dedicated/separate processor runs the algorithm 26 orportion thereof for shifting and adding corresponding pixel values fromat least two different frames to compose an image pixel in the panoramicimage corresponding to a “virtual” speed profile different from thepredetermined speed profile and a different (non-predetermined) layer.The speed profile relates to the speed at which the imaging device isactually scanning.

The present system 10 takes the frame data 40 generated during a singleexposure to selectively compose different types of images form the sameframe data 40. Preferably, the system 10 composes at least two of agroup of images selected from the group of reconstructable imagesconsisting of: a predetermined dental panoramic layer image; an imagecomprising part of a non-predetermined dental panoramic layer image andthe predetermined panoramic layer image; a transverse slice to aselected part of a dental panoramic layer image; and a 3-Dreconstruction of a volume corresponding to some part of a dentalpanoramic layer. With this feature, a selectable part of thepredetermined layer can be replaced with an analogous part of adifferent non-predetermined layer, to accomplish the re-focusing featureof the present invention. This how auto-focusing/manualfocusing/re-focusing feature of the present system 10 is enabled.

After the display and processing, the data set 132 can be stored on ahard drive, a CD, a DVD and/or other non-volatile digital storage media.The use of RAM 18 to store the data temporarily and the fastreconstruction algorithm 26 mentioned above allows the image 12 to bereconstructed and displayed no later than 10 seconds from the end of theexposure and usually within 5 seconds. In fact, the image 12 may bereconstructed from 750 MB of single frame data and displayed inreal-time with a minimal delay (the delay needed for causality) duringthe actual exposure.

Example II

In another embodiment, the X-ray imaging device 14 produced multipleframes 40 during an exposure with time intervals during which thedetector pixels were shifted by at least half a pixel length or more inthe direction of scanning 104. Additionally, the detector pixels wereshifted by at least half a pixel size, but less than the size w of afull pixel in the direction of scanning.

In accordance with another embodiment of the invention, all theindividual frames 40 are stored temporarily in a RAM-type fast memory18, and therefore it is possible to reconstruct the final image 12 witha modified position profile, after the actual exposure and after theinitially displayed panoramic image 12. It is known of course, that thedata can additionally be stored long term on a data storage system 22such as a hard drive, CD or DVD and retrieved later back into fastmemory. However, storing all the data on RAM 18 makes processing fastand efficient. Such is now possible because the amount of data needed tobe stored has been significantly reduced given the amount of overlapbetween frames, and because of the elongated shape of the active area520. Consequently, there is no need to wait for data to be downloaded, aprocess that normally takes several seconds. This, however, is notpossible with TDI-type imaging devices, because the positionsynchronization has already been done in the camera hardware in analogdomain, and thus cannot be modified.

The shifted amount 76 between consecutive frames 40 is normallydetermined from the position information gathered during themeasurement. This should give a panoramic image 12 with thelayer-of-interest 52 in full focus. Unfortunately, due to misalignmentof the patient 72, or patient motion, different jaw profile or for manyother reasons, there are very often portions in the panoramic image 12that are out-of-focus or blurred. The shift 76 between consecutiveframes 40 (i.e., the speed of the movement in the imaging plane 12)determines which layer 99 is well focused. If the movement speed of thecamera 14 with respect to the X-ray source 16 is Vcamera, the distancebetween X-ray source focal point 36 and the imaging plane 12 is d₁, andthe layer of interest 52 is at distance d₂ from the focal point 36, thenthe required speed V_(shift) for the shift-and-add algorithm 26 isdetermined according to equation (1):V _(shift)=(d ₁ /d ₂)×Vcamera  (1).

Thus, by modifying the shifting amount 76, a different layer 99 can befocused. In theory; any layer can be in focus, but the finite pixel sizesets a limitation on how sharply a layer appears. If the shifting speed76 is more than a pixel 53 per frame, the image resolution is degradedin the process. The shifting amount 76 can be modulated by softwareeither globally or locally to allow either a completely different layer99 to be displayed or to modify an existing layer to improve thesharpness in out-of-focus regions, which is usually the case in dentalpanoramic X-ray imaging.

The shift speed 76 cannot only be modified on a column-by-column basis.In addition, the speed 76 can vary on a row-by-row basis (i.e., everypart of the image 12 might have a different speed). This enablesbringing into focus of both upper 180 and lower teeth 182, for example,when the patient 19 has an incorrect bite (i.e., front and back teethare not on the same vertical plane). This is an important feature of thepresent system 10, and can have tremendous impact on today's practice ofdental radiology, because the blurred part of the image 12 can bebrought into focus and displayed with the rest of the original panoramicimage. Therefore, it is no longer necessary to re-expose the patient 19a second, much less a third time. In this manner, the layer-of-interest52 can be modified by altering the shifting amount 76 in theshift-and-add algorithm 26.

In accordance with another embodiment of the present invention, theoptimal speed profile 186 (see FIG. 12) may be calculated. Additionally,the present system 10 is adaptable to create panoramic dental images 12which have a focus depth selectably different in some but not in allportions when compared to the focus depth of a predetermined panoramicimage.

In still another embodiment, the system 10 is adapted to createpanoramic dental images 12 in which the means of using multiple frames40 comprises sub-pixel shifting and the adding of pixel values fromdifferent frames.

In another embodiment, the system 10 includes a means for creating atransverse dental image slice 224. This means uses multiple frames 40 toform the transverse image 224 by combining vertical pixel rows referringto the same physical transverse slice from multiple panoramic images.

Referring to FIG. 10, in another embodiment, the dental X-ray imagingsystem 10 of the invention includes an algorithm 400 which uses themultiple frames 40 to compose a transverse slice 224 with respect to apanoramic image. The algorithm 400 includes subroutines 400 a and 400 b.In the first subroutine 400 a, in a first step 402, frame data 304 isused to reset the change in velocity ΔV to the original change invelocity ΔVorig. In a second step 404, the user specifies a region ofinterest. In a third step 406, the region of interest is reconstructedat the original speed ΔVorig plus the change in velocity ΔV. In a fourthstep 410, the reconstructed region of interest is resized to a fixedsize. In a fifth step 412, the resized reconstructed region of interestis pushed to the image layer stack. In a sixth step 414, a blur functionis calculated and stored. In a seventh step 416, if delta velocity ΔV isgreater than a particular limit, then the stack is processed in atransverse slice calculation subroutine 400 b; otherwise, delta velocityΔV is increased and the process returns to the third step 406 andcontinues. The transverse slice subroutine 400 thus forms a transverseimage slice 224 in addition to a panoramic layer 60 using the frames 40accumulated during the same exposure. In transverse imaging, thelayer-of-interest 69 is perpendicular to a panoramic layer 52. Usuallythis is done as described earlier, but in accordance with thisembodiment of the invention, this is performed more elegantly.

As described earlier, multiple panoramic layers can be calculated from asingle measurement data set. By intelligently calculating correct speedmodulation function, a transverse slice image 224 can be formed byconcatenating the corresponding rows from individual panoramic layers inorder of increasing depth. The algorithm 400 b has the following steps:In a first step, method 400 b′ is applied to calculate multiplepanoramic images, stored in a stack. In a second step 400 b″, thecontribution of the 3D physical structure at different distances iscalculated for every panoramic image 12. Every panoramic image 12contains the image of the 3D physical model not only at thelayer-of-interest, but also in front of and in back of it. This can bemodeled using a blur function. In this step 400 b′″, the blurring isreversed using a de-convolution method, and thus the true image atdifferent panoramic layers without crosstalk between neighboring layersis formed. The transverse image 224, formed by concatenating differentpanoramic layers 60, may now be displayed. Contrary to U.S. Pat. No.6,496,557, which describes a system where the imaging plane isperpendicular or roughly perpendicular to the direction of radiation,the present invention discloses a system 10 which provides a layer 60parallel (or close to parallel) to the direction of radiation.

Referring now to FIG. 11, additionally, an imaging method 229 can beused to provide limited volumetric 3D images. The method 229 is aniterative algorithm, which, in step 229 a, uses the geometry data (i.e.,3D location of X-ray source and the detector and the related movementprofiles) to form re-projection data (i.e., estimates of the projectedframes 40 based on the present 3D model). Then, in step 229 b, thesoftware calculates the error between measured and re-projected frames40. In step 229 c, this error is used to update the current 3D estimate.This operation is applied to a region-of-interest specified by the user.Because of the limited number of views, narrow projection rotationalangles and narrow projection width, it is very important to use priordata in the reconstruction. Prior data is used to set restrictions onthe 3D model, like smoothness, to produce and unique and meaningfulresult. The 3D image obtained is not comparable to full CT images inquality, but is sufficient for dental operations.

An object of the invention is to produce selectively predetermineddental panoramic image layers, dental panoramic X-ray images ofdifferent layers, dental transverse X-ray images and dental X-ray imagesfrom a frame stream produced by a high-speed, X-ray digital imagingdevice.

In an advantage, the system's 10 functioning on data from a singleexposure spares the patient multiple exposures and allows for the firsttime effectively risk free exposures in dental radiology. Such system 10has unique advantages and offers a breakthrough in the field of dentalradiology.

In another advantage, the dentist is able with a single system 10 andsingle exposures to do examinations that previously required at leasttwo if not more systems totaling a multiple in cost and a multiple ofrisk in patient diagnosis and treatment. Examinations become safer andless expensive for the patients who now only need take one exposure.

In another advantage, the system 10 applies little more radiation thanthe radiation dose used in a regular dental panoramic exposure andshould employ X-ray scan mechanics that operate in continuous movement.

In another advantage, continuous movement means that the speed ofscanning V is greater than zero at all times during the scan. The speedneed not be constant.

In an advantage, CdTe or CdZnTe based digital imaging devices have anexcellent sensitivity and absorb 95% of the incoming x-rays at dentalapplication energies (i.e., from 10 kV up to 90 kV X-ray tube load).

In another advantage, the need for non-continuous, step-wise scans areeliminated, thus reducing the radiation doses and eliminating the longerstep-wise scans, which create higher risk and discomfort to the patient.Because a continuous fast X-ray scan is possible, one does not needseparate specialized dental equipment other than the normal panoramicX-ray units.

In another advantage, a system 10 and method are provided of combiningdata from a single exposure to not only reconstruct a panoramic layer ofinterest, but also to be able to correct part of the image that isblurred and furthermore produce transverse image slices and 3D images.

In another advantage, the system 10 and method of the invention producea variety of formats of panoramic images from a high-speed, X-raydigital imaging device.

Multiple variations and modifications are possible in the embodiments ofthe invention described here. Although certain illustrative embodimentsof the invention have been shown and described here, a wide range ofmodifications, changes, and substitutions is contemplated in theforegoing disclosure. In some instances, some features of the presentinvention may be employed without a corresponding use of the otherfeatures. Accordingly, it is appropriate that the foregoing descriptionbe construed broadly and understood as being given by way ofillustration and example only, the spirit and scope of the inventionbeing limited only by the appended claims.

Glossary of Terms

CCD Charge coupled device: an imaging device capable of converting lightto electric signals. In X-ray imaging, a CCD is usually coupled with ascintillator.

CT Computed tomography: a method of calculating full volumetric 3D datafrom multiple projections covering the full 360 degree rotationalcircle.

Imaging device: a device with multiple elements (pixels) able to convertX-ray radiation to a digital image.

Pixel column: a group of pixels perpendicular to a pixel row, i.e.,pixels along a line perpendicular to the direction of movement.

Pixel row: a group of pixels in an imaging device in the movementdirection. For example, if the camera is rotating around the verticalaxis, a pixel row refers to pixels along a horizontal line.

Scintillator: a device able to convert X-ray radiation (for examplex-rays and gamma) to light. A scintillator is usually coupled with a CCDto provide a device able to convert radiation to electric signals.

TDI Time-delayed Integration: a method in which a single scanned 2Dimage is formed by concatenating multiple ID line images.

1. An extra-oral dental x-ray imaging system comprising: a. a single x-ray source adapted for generating x-rays for an exposure of such x-rays to an object to be imaged; b. a frame mode x-ray imaging device adapted to produce multiple frames during at least part of the exposure, the x-ray imaging device having an active area with a long dimension m and a short dimension n and wherein m/n>1.5, the geometry between the x-ray source and the detector being fixed; c. at least one rotational axis around which at least one of the x-ray source and the imaging device rotates along a spline, the axis being located somewhere between the x-ray source focal point and the x-ray imaging device; d. a manipulator adapted for moving said at least one of the imaging device and the x-ray source between the multiple frames during the exposure about the at least one rotational axis; and e. a processing device for taking inputs of the multiple frames to compose a panoramic image of a layer of the object with a focus depth which is different in a region of interest from a focus depth corresponding to a predetermined panoramic image, wherein the focus depth for the region of interest is determined automatically, wherein the focus depth for the region of interest is determined by the processing device automatically by: calculating plural layers using a laminographic reconstruction of the plural layers; calculating a sharpness measure for each of the plural calculated layers; and based on the calculated sharpness measure, choosing a sharpest layer from among the plural calculated layers for the region of interest to provide for and display a corrected layer for the region of interest defined for said panoramic image as a predetermined anatomical region defined by a predefined geometric path of the single source and detector, patient type, and a predetermined speed profile.
 2. The extra-oral dental x-ray imaging system of claim 1, wherein the sharpness measure is one of a measure of contrast and a measure of roughness.
 3. The extra-oral dental x-ray imaging system of claim 1, wherein the laminographic reconstruction by the processing device uses said multiple frames and executes pixel shifting or sub-pixel shifting and adding of pixel values from different frames to calculate the plural layers.
 4. The extra-oral dental x-ray imaging system of claim 3, wherein, the pixel shifting or sub-pixel shifting is applied selectively on at least one of i) a column-by-column basis, and ii) a row-by-row basis, and the amount of shifting can be selectively different for different parts of the panoramic image.
 5. The extra-oral dental x-ray imaging system of claim 1, further comprising: a memory storing and holding the frames produced, with the stored and held frames being individually selectively accessible, wherein the processing device permits retrieval and a display of the frames as a reconstructed panoramic image within 10 seconds of an end of exposure of the frame.
 6. The extra-oral dental X-ray imaging system of claim 1, wherein the processing device composes a transverse slice with respect to a panoramic layer image as a reconstructed transverse slice image within 10 seconds of an end of exposure of the frame.
 7. The extra-oral dental X-ray imaging system of claim 1, wherein a focus depth of a panoramic image is different in some parts of the image when compared to a focus depth of analogous parts of a predetermined panoramic image.
 8. The extra-oral dental X-ray imaging system of claim 1, wherein the X-ray imaging device is adapted to produce at least 300 frames per second.
 9. The extra-oral dental X-ray imaging system of claim 1, wherein the X-ray imaging device comprises a Cd—Te radiation detector.
 10. The extra-oral dental X-ray imaging system of claim 1, wherein the X-ray imaging device comprises a Cd—Zn—Te radiation detector.
 11. The extra-oral dental X-ray imaging system of claim 1, wherein the X-ray imaging device comprises a scintillator radiation detector.
 12. The extra-oral dental X-ray imaging system of claim 1, wherein the X-ray imaging device comprises a CMOS.
 13. The extra-oral dental X-ray imaging system of claim 1, wherein the X-ray source is adapted to move continuously with a variable speed profile.
 14. The extra-oral dental x-ray imaging system of claim 3, wherein, the laminographic reconstruction of the plural layers is a time-compensated laminographic reconstruction of the plural layers. 